The goal of this project is to examine the role of auditory cortex in rhesus monkeys for discrimination of species-specific vocalizations. Results from lesion and electrophysiological work suggest that there are specific regions of macaque auditory cortex devoted to vocalization analysis. Destruction of auditory cortex impairs vocalization discrimination in at least one macaque species, the Japanese monkey. Neurons in the lateral belt region of macaque cortex show greater responsiveness to both band-limited noise and harmonically complex coo vocalizations, compared to pure tones, and this responsiveness is topographically organized. We will examine the effects of restricted reversible inactivation of auditory cortex, using the GABA agonist muscimol, on the ability of rhesus monkeys to discriminate natural, species-specific vocalizations, including synthesized parametric variations of these calls. We will determine the extent of cortical involvement, and the features relevant for this acoustic analysis. This technique will permit comparison of the effects of varying the location and extent of inactivation over sessions. It will also allow comparison of unilateral and bilateral inactivation, in the same subject, and so address the question of whether vocalization analysis is lateralized in the rhesus as has been demonstrated for the Japanese macaque. On a discrete-trial operant task, subjects will be required to discriminate a particular vocalization or synthesized call from other exemplars on a given trial. Following craniotomy and implantation of bilateral recording chambers, auditory cortex (AI, R and the lateral belt region) will be mapped and, using a grid, a guide-tube array will be positioned within the defined fields. During subsequent testing we will assess the effects of muscimol application on discrimination. By varying the volume and location of drug injection we will be able to vary the extent and region of inactivation. This will permit us to examine the relationship between cortical inactivation and call structure on the macaques' discrimination abilities. The results will be important in understanding the cortical role in the analysis of complex acoustic signals such as natural vocalizations. This project should also serve as a useful model system for understanding mechanisms of speech perception and impairment in humans.